JP2002008583A - Mass spectrometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an mass spectrometer which reduces adverse effects of neutral particles or charged droplets by dry gas. SOLUTION: With a mass spectrometer provided with an ion source which ionizes eluate from liquid chromatograph at an atmosphere and a mass spectrometry part which carries out mass spectrometry on ion under high vacuum generated by the ion source, the ion source is provided with a spray means for spraying the eluate, an exhaust nozzle formed so as to cover the spray means and supplying heated gas from the direction opposite to spraying direction of discharge liquid, a throttling plate for throttling gas flow around the exhaust nozzle, and a case furnished with a through-hole for exhausting ion toward the mass spectrometry part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a mass spectrometer,
In particular, the present invention relates to a mass spectrometer using a liquid chromatograph connected thereto.

[0002]

2. Description of the Related Art A mass spectrometer for measuring an effluent from a liquid chromatograph measures a trace amount of an organic compound dissolved in a liquid with high sensitivity. Heretofore, mass spectrometers using a sector-shaped magnetic field or quadrupole mass spectrometers have been widely used as mass spectrometers for such applications. Recently, attention has been paid to quadrupole mass spectrometers (rod type, ion trap type, etc.) as inexpensive mass spectrometers, and they have been adopted as liquid chromatograph direct-coupled mass spectrometers (hereinafter abbreviated as LC / MS). It has become.

FIG. 1 shows an example of LC / MS using an ion trap type mass spectrometer.

[0004] The mobile phase solvent stored in the solvent bottle 1 is sent to the analysis column 4 via the inlet 3 by the pump 2. The sample is introduced from the injection port 3 by a micro syringe or the like. The introduced sample is separated for each component while traveling through the analytical column 4. The separated components are separated by LC / M in the space covered by the metal cover 41 together with the mobile phase solvent.
It is sent to the S interface (ion source). L
Although there are various types of C / MS interface units, an example using an electrospray method (hereinafter abbreviated as ESI) will be described here.

[0005] The sample component solution leaving the analysis column 4 is sent to an ESI probe 5 to which a high voltage is applied. From the tip of the ESI probe 5, it is sprayed into the atmosphere as a charged droplet. The sprayed droplets repeatedly collide with atmospheric molecules, the diameter of the droplets becomes smaller, and finally ions are released into the atmosphere.

[0006] The generated ions are exhausted from the pores 6 provided at the top of the skimmer by the vacuum pump 7 and introduced into the chamber 30 (mass analyzer) in which the mass spectrometer is placed. The ions introduced into the chamber 30 are sent to the inside of the ion trap 40 via the ion guide or the octapole lens 8. The ion trap has two end cap electrodes 9 and 10, one donut-shaped ring electrode 11, and a spacer 3 made of glass or ceramic.
1, 32, etc. These three electrodes 9, 1
The cross section at 0, 11 is hyperbolic. The ions sent into this ion trap interior 40 are
Is stably captured in the ion trap inside 40 by the high frequency of about 1 MHz applied to the ion trap. A mass spectrometer using an ion trap can integrate ions inside the ion trap 40 while introducing ions. Inside the ion trap 4
The ions stored in 0 are swept out of the high-frequency voltage (amplitude) applied to the ring electrode 11, so that the ions are removed from the ion trap through holes formed at the centers of the end cap electrodes 9 and 10 in ascending order of mass. Released. The emitted ions are detected by the detector 12, and a mass spectrum is obtained by the data processor 13.

[0007]

The quadrupole mass spectrometer (rod type, ion trap type, etc.) is a small-sized apparatus, but can perform highly sensitive measurement. However,
The quadrupole mass spectrometer often has a structure in which the distance from the ion source to the mass spectrometer in the vacuum chamber is short. Therefore, the air or mobile phase solvent introduced into the vacuum chamber together with the ions undergoes rapid diffusion and is scattered as neutral particles in the vacuum chamber. In addition, some of them become ions due to having electric charge (generally called charged droplets), and are scattered in the vacuum chamber simultaneously with the neutral particles. These neutral particles and charged droplets become random signals and are taken into the data processor together with the mass spectrum. This random signal is worthless and becomes part of the noise. The quadrupole mass spectrometer can perform highly sensitive measurement, but under the measurement conditions in which a random signal is likely to be generated, noise increases, which may interfere with high-sensitivity measurement.

For highly sensitive measurements, large droplets such as neutral particles and charged droplets having a diameter much larger than the atomized sample solution (up to several tens of μm in diameter) are formed.
It does not have to reach the mass spectrometer or the detector. Therefore, if the ion source has a drying ability and it is dried and removed before huge neutral particles and charged droplets enter the vacuum chamber,
These can be prevented from reaching the mass spectrometer and the detector, and the occurrence of noise can be prevented.

Japanese Patent Application Laid-Open No. 6-215727 discloses a device having a means for drying such droplets.
Japanese Unexamined Patent Publication No. Hei 9-509781, JP-A-11-1423
No. 72 publication.

In each of these examples, an ion source under atmospheric pressure is supplied with a drying gas from a direction opposite to the direction of spray of the effluent from the liquid chromatograph, and attempts to dry droplets. However, in any of the examples, the role of the drying gas is to reduce the influence of the droplet, and it is inevitable that the droplet is introduced into the mass spectrometer together with the sample ions.
Therefore, in these examples, the influence of the droplet is reduced by a configuration other than the dry gas.

An object of the present invention is to reduce the influence of neutral particles and charged droplets by using a drying gas, unlike the above-mentioned known examples, and to further reduce the drying and drying of the droplets compared with the conventional structure.
An object of the present invention is to provide a mass spectrometer capable of enhancing the effect of removal.

[0012]

SUMMARY OF THE INVENTION In order to achieve the above object, a feature of the present invention is to provide an ion source for ionizing an effluent from a liquid chromatograph at atmospheric pressure, and an ion source generated by the ion source. In a mass spectrometer provided with a mass spectrometer that performs mass spectrometry under high vacuum by being introduced, the ion source is formed so as to cover the spraying means for spraying the effluent, and the spraying means, and A housing having an outlet for supplying a gas heated from a direction opposite to the spray direction of the effluent, a throttle plate for narrowing the gas flow near the outlet, and a through-hole for discharging ions in the direction of the mass analyzer. It had a body.

[0013]

FIG. 2 shows a first embodiment of the present invention. FIG. 2 shows an ion source unit which is a characteristic configuration of the present invention. The configuration of other mass spectrometry units and the like is common to the example of FIG.

The ion source of the present invention is characterized in that a cylinder 22 is provided in a cover 41. Hereinafter, the configuration of the ion source of the present invention will be described.

The cylinder 22 is disposed at a position so as to cover the eluate 24 from the liquid chromatograph sprayed from the ESI probe 5, and a nitrogen gas (90% or more in purity) from the direction opposite to the spray direction of the eluate 24. Hereinafter, the AUX gas) 27 is blown out. As the specific size, the inner size is about 50 mm or less in diameter,
The length is about 100 mm or less, and the cross-sectional area is at least two orders of magnitude larger than the eluate passage portion of the ESI probe 5. With such a size, the sprayed eluate 24 can be suppressed from being diffused in the ion source to lower the gas concentration, and can be efficiently mixed with the AUX gas 27. .

The AUX gas 27 is a heater 2 for the AUX gas.
After being heated to about 200 to 400 ° C. at 5, it is supplied at a flow rate of about 10 to 20 liters per minute, and is blown from the gas outlet 23 at a low speed of about several m / s. The blown AUX gas 27 heats the temperature of the atmosphere in the cylinder 22 to the same level as the AUX gas 27. A throttle plate 28 is provided in the vicinity of the gas outlet 23 to restrict the blown AUX gas flow and to spray the eluate 2
4 from the front. The AUX gas 27 may be another gas such as air as long as it is an inert gas.

The eluate 24 is prepared from the ESI probe 5 at a concentration of 0.2 μm.
Assist gas 2 at about 5-9 L / min, normal temperature to 100 ° C
Together with 6, the liquid is sprayed into the cylinder 22 at a linear velocity of 50 m / s or more to form a positive pressure atmosphere and a turbulent flow (vortex) in the cylinder 22. At this point, the sprayed eluate 24
Is an atomized state, and is a large droplet having a diameter of about several tens μm on average.

The sprayed eluate 24 entrains the heated AUX gas 27 supplied from the outlet 23 due to the vortex generated by the turbulent flow, so that the eluate 24 travels about 200 to 40.
Under an environment of 0 ° C., heat is efficiently exchanged while being mixed and stirred with the AUX gas 27, and the diameter is several tens μm within several ms or less.
The state changes to a state in which only ions are extracted from the m droplets (atomized state) into the gas phase (ion evaporation). The ion-evaporated sample becomes single charged particles (ions) in the gas phase, is extruded toward the skimmer electrode 6 by the positive pressure in the cylinder 22, and is taken into the mass spectrometer through the pores in the skimmer electrode 6. After that, mass spectrometry is performed.

Here, the speed at which the eluate 24 is sprayed into the cylinder 22 is desirably a speed that produces a speed difference of 10 times or more relative to the blowing speed of the AUX gas 27. By having such a speed difference, the AUX gas 27 is efficiently entrained and the eluate 24 is evenly heated while maintaining the skimmer electrode 6 at a certain speed.
It is possible to guide ions in the direction. That is, AUX
The effect of drying the droplets by the gas 27 is further improved.

The cylinder 22 is made of metal,
Alternatively, the inner surface is formed by plating or depositing a metal to have conductivity. This is to forcibly keep the potential at a specific potential, whereby charge-up can be prevented.

In the embodiment shown in FIG. 2, an example in which ESI is used as the ion source is shown.
I (sonic spray method) may be used. FIG. 3 shows an example in which SSI is used for the ion source.

The vaporized sample gas pushed out from the cylinder 22 is heated to 200 ° C. by the influence of the AUX gas 27.
Because of the high temperature of 400 ° C., this is
Directly, the surface and the inner surface of the skimmer electrode 6 are overheated to a control temperature or higher, and the sample gas is thermally decomposed while passing through the skimmer electrode, thereby lowering the measurement sensitivity.

Therefore, in the present invention, means for cooling the skimmer electrode 6 is provided. As a specific example, as shown in FIGS. 2 and 3, a metal heat shield plate 21 is attached to the skimmer electrode 6, and a nitrogen gas 33 of 100 ° C. or less is blown per minute from a laterally opened hole. The nitrogen gas 33 is supplied on the surface of the skimmer electrode 6 by supplying 2 to 3 liters.
The temperature is controlled within the range of 00 ° C. This allows
It is possible to prevent thermal decomposition of the sample.

FIG. 4 shows another embodiment of the skimmer electrode 6 cooling means according to the present invention.

In the example shown in FIG. 4, a radiation fin 29 made of metal such as aluminum is attached to the skimmer electrode 6.

According to this embodiment, there is no need to supply a cooling gas as in the examples of FIGS. 2 and 3, which is advantageous in terms of cost and maintenance.

FIG. 5 shows another embodiment of the cooling means for the skimmer electrode 6 according to the present invention.

In the example shown in FIG. 5, a cooling unit including a Peltier element 35 and a control power supply 36 is attached to the skimmer electrode 6 to perform cooling.

Thus, it is possible to easily control the cooling state by controlling the control power supply 36.

FIG. 6 shows another embodiment of the cooling means for the skimmer electrode 6 according to the present invention.

In the example shown in FIG. 6, a cooling water hole 37 is formed in the skimmer electrode 6, and cooling water cooled by a cold chiller unit 39 is supplied to the hole through a pipe 38 to cool the skimmer electrode 6. Is what you do. Also in the present embodiment, it is possible to easily control the cooling state by controlling the cooling chiller unit 39.

[0032]

According to the present invention, drying of giant droplets composed of neutral particles and charged droplets generated when a sample solution is sprayed by an ion source can be removed by heating with an inert gas. This makes it possible to remove random noise and improve S / N.

In addition, the overheating of the skimmer electrode caused by heating the inert gas can be reduced by using the above-mentioned various cooling means in combination.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional apparatus configuration.

FIG. 2 is a diagram showing a first embodiment according to the present invention.

FIG. 3 is a diagram showing a configuration example when an ion source is changed to SSI.

FIG. 4 is a view showing another embodiment of a skimmer electrode.

FIG. 5 is a view showing another embodiment of the skimmer electrode.

FIG. 6 is a view showing another embodiment of a skimmer electrode.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Solvent bottle, 2 ... Pump, 3 ... Sample inlet, 4 ... Analysis column, 5 ... ESI probe, 6 ... Skimmer electrode, 7 ... Vacuum pump, 8 ... Electrostatic ion guide, 9, 10 ... End cap electrode , 11 ... Ring electrode, 12 ... Detector, 13
... data processing device, 21 ... heat shielding plate, 22 ... cylinder, 23 ... gas outlet, 24 ... electrostatically sprayed eluate, 25 ... heater for AUX gas, 28 ... throttle plate, 29 ...
Radiating fins, 30 vacuum chamber, 31, 32 glass or ceramic spacer, 35 peltier element, 36 control power supply, 37 cooling water hole, 38
Pipe, 39: chiller unit, 40: inside ion trap, 41: metal cover, 42: SSI ion source.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadao Mimura 882 Momo, Oaza-shi, Hitachinaka City, Ibaraki Pref. Within the Measuring Instruments Group, Hitachi, Ltd. F term in Hitachi Central Research Laboratory (reference) 5C038 EF04 EF26 GG01 GH05

Claims (11)

[Claims] 1. An ion source for ionizing an eluate from a liquid chromatograph under atmospheric pressure, and a mass analyzer for introducing ions generated by the ion source and performing mass analysis under high vacuum. In the mass spectrometer described above, the ion source is provided with a spraying means for spraying the effluent, and supplies a gas formed to cover the spraying means and heated from a direction opposite to a spraying direction of the eluate. An outlet, and a throttle plate for restricting a gas flow near the outlet,
A mass spectrometer comprising a housing having a through-hole for discharging ions toward the mass spectrometer. 2. The mass spectrometer according to claim 1, wherein the size of the inside of the housing is 50 mm or less in diameter and 100 mm or less in length. 3. The mass spectrometer according to claim 1, wherein the pressure in the housing is higher than the atmospheric pressure. 4. The mass spectrometer according to claim 1, wherein said ion source is an electrospray (ESI) method or a sonic spray (SSI) method. 5. The mass spectrometer according to claim 1, wherein the inner surface of the housing is formed of a conductive material. 6. The mass spectrometer according to claim 1, wherein each of the gas supplied from the outlet and the effluent is sprayed such that a relative velocity difference becomes 10 times or more. . 7. The skimmer according to claim 2, further comprising a skimmer electrode having pores for guiding ions into the mass analyzer between the housing and the mass analyzer, further reducing the temperature of the skimmer electrode. A mass spectrometer comprising a cooling means. 8. The mass spectrometer according to claim 8, wherein said cooling means supplies air or nitrogen gas or an inert gas such as He or Ar to the skimmer electrode at a temperature of 100 ° C. or less. 9. A mass spectrometer according to claim 8, wherein said cooling means comprises a Peltier element provided on the surface of said skimmer electrode and a power supply for controlling said element. 10. The mass spectrometer according to claim 8, wherein said cooling means is a cooling fin provided on a surface of said skimmer electrode. 11. The mass spectrometer according to claim 8, wherein said cooling means sends cooling water into a cooling water flow path provided in said skimmer electrode.